ASSOCIATIONS OF Pu AND OTHER ACTINIDES IN SOILS idi 



comparison, the ratio for the two sizes in the ML samples were 2.34 and 0.29 in the 

 sediment sample and 2.42 and 0.60 in the soil sample. These results show that the ML 

 samples are enriched in the fine-clay size fraction. 



Tamura (1976) reported on the size association of plutonium in a RF soil taken from 

 the 5- to 10-cm depth near the spill site. The activity/size ratio was 2.26 in the clay 

 fraction and 1.26 in the coarse-silt fraction. In another sample taken 1 km east of the spill 

 site, the ratios of the two sizes were 3.20 and 0.98, respectively (Tamura, 1977a). 



The size associations of the plutonium show that in the safety shot sample of NTS the 

 clay-size fraction is not enriched in plutonium; at the other sites the clay size is relatively 

 enriched. However, the association with clay in the enriched samples does not necessarily 

 mean high acid solubility. The 8M nitric acid extraction at room temperature revealed 

 that the ML and ORNL samples are quite soluble (over 60%); the RF sample was less 

 soluble (15 to 20%). The difference in the acid solubility is likely due to the initial 

 soluble form in the ML and ORNL releases and the metallic nature of the RF sample. 



Implication of Particle Size Association 



Tamura (1977b) attempted to evaluate the significance of the size association of 

 plutonium on soil particles in terms of potential hazard due to resuspension and 

 inhalation of contaminated particles. He considered the soil particle size association of 

 the plutonium, the depositional character of the different particle sizes in the pulmonary 

 compartment of the lung, and the fraction of activity in the resuspendible fraction in the 

 soil. This initial attempt did not include considerations of soil erodibility, vegetation, 

 field size, and surface-rougliness factors, which are important in wind erosion of soils 

 (Skidmore, 1976). 



Table 5 shows the soil plutonium indexes calculated from the three factors for the 

 four contaminated sites. The less than 125-/im size is considered to be the resuspendible 

 fracfion; others have suggested the less than lOO-jitm sizes (Chepil, 1945; Healy, 1974), 

 but the available data are given for the slightly larger size. The soil activity factor is 

 defined as the activity per unit weight of mass for each size fraction. This factor is derived 

 by dividing the activity portion of a given size by the mass contribution of that size; it 

 therefore weights the activity in the different potentially inhalable sizes. 



Table 5 also gives the depositional fraction derived by the Task Group on Lung 

 Dynamics (1966) and the depositional factor derived as a product of the soil activity 

 factor and the depositional fraction. The depositional percentage of the larger 

 resuspendible sizes is relatively low; most of these particles are filtered by the upper 

 respiratory tract and have a short biological half-life (Task Group on Lung Dynamics, 

 1966). Also included in Table 5 is the fraction of the activity found in the < 125-/am sizes. 

 The high percentage results in a small effect on the final soil factor. The activity 

 distribution was detemiined by using water suspension and either ultrasonic treatment or 

 chemical dispersant (ML sample). Thus the actual association of the plutonium in the soil 

 may be different and should be evaluated. 



The final soil index shows a range of 0.52 for the NTS sample to 1.26 for the RF 

 sample. This implies that the plutonium in the soil at the RF site is potenrially about 2.4 

 times as hazardous in terms of the inhalation pathway. It should be emphasized that the 

 number of samples is limited, and the factors may change with more information. 

 Furthermore, the erodibility and other factors of the soils were not evaluated; hence, 

 until these factors are evaluated and larger numbers of samples are investigated, the 

 indexes are only tentative. 



